The paper said the victim of the attack had not been named. However, it said it understood he was a “young university student from the United States who had been observing the animals at the reserve for several weeks.”

Jeffrey Wicks, a spokesman for private ambulance firm Netcare911, told the Telegraph that witnesses said the man was leading a group of tourists when the attack happened.

"A ranger at a chimpanzee sanctuary near Nelspruit is fighting for his life after he was attacked by two frenzied animals while leading a tour group at the park this afternoon," he added. "According to eyewitnesses, two chimpanzees grabbed the man by his feet and pulled him under the perimeter fence and into the enclosure."

Armed escorts for paramedicsParamedics needed armed escorts as they went in to treat the victim, NBC’s Rohit Kachroo reported. It was unclear whether this caused any delay.

The victim was stabilized at the scene and taken by ambulance to a private hospital in Nelspruit, NBC said. There have been no similar attacks at the reserve, which opened more than six years ago.

David Oosthuizen, Jane Goodall Institute executive director, confirmed the reserve was on lock down following the incident, The Telegraph said.

NBC's Meredith Vieira sits down with Charla Nash, who recently underwent a face transplant that's helped her regain the life she had before being brutally attacked by a chimp.

"We understand that the gentleman is stable and we really feel for him," he told the paper. "This has been very upsetting for everyone – it is just horrific. We are an organization that's respected worldwide for the work we do so anything like this is very bad."